NC for this as don't want to be outed.
Apologies in advance if this is long and rambling.
Background: my DB and SIL have had problems in their marriage for a while. They have 3 young DCs (under 3), problems have arisen as DB doesn't pull his weight and can be lazy, selfish and manipulative when challenged about his behaviour. I hear all of this from SIL who regularly complains to me about him (although I have also actually witnessed it myself on a few occasions). She is often in tears because of arguments they have had (and particularly cruel things he has said to her) and apologises for always coming to me about it, but says she can't go to her own family for fear they will turn against DB. Besides, she knows I know what can be like.
Rest of family inc DM and my other two DBs all aware of the situation. They acknowledge DB is in the wrong, as do I, but we all try to stay out of it and support SIL and DCs the best we can without interfering in their relationship.
Jump to recent events: DB, SIL and their DCs, and me, DH and our DD went on holiday with some friends and their DCs. DB was fairly hands off and lazy all week. SIL did everything with kids and it was noted by everyone there. He snapped at me when I suggested he did something with the kids. Things came to a head one night when he was drunk and was really aggressive and rude to me. I was 32 weeks pg and got v upset. Usually I would've ignored it, but I ended up in floods of tears and it spoilt the holiday.
I came home vowing not to go away with him again but it is DMs 60th birthday coming up. As part of celebrations, whole family are supposed to be going away next weekend (after that there is a birthday lunch and a party at DMs house the following weekend, so it isn't only celebration). I will be 37 weeks pregnant. I said to DM I really didn't want to go away with DB but she got upset so I said I would go.
However, this week DB and SIL have had another row (started because his tea wasn't on the table when he got in from work!) which resulted in SIL going to her parents with the kids for the night. She texted me to tell me and cancel plans we had made for the following day. She seemed v upset and said she just needed a break from DB.
The next day I spoke to DM, who happened to ask if I had had a nice time with SIL. I told her she had cancelled and why. Next thing I know, I receive a really nasty text fromDB asking why I am deliberately trying to upset DM by telling her SIL had spent night at her parents. He is accusing me of sticking my nose in etc and trying to make out that I am shit stirring etc.
I am really pissed off. I don't want to be in the middle of their relationship issues and I only told DM as she asked about SIL. And I really don't want to go away with them all next weekend. This hasn't been an easy pregnancy and I feel really stressed at the thought of how tense it will be. I also feel really tearful about the whole thing, which I know is hormones but I just want to disengage from all of it.
However, I know it will really upset DM if I don't go. AIBU not to go?